1. Field of the Invention
The present invention relates to a liquid ejecting apparatus for ejecting liquid drops from a nozzle opening thereof. As a typical example of a conventional liquid ejecting apparatus, there is an ink jet recording apparatus having an ink jet recording head for image recording available. As other liquid ejecting apparatuses, for example, an apparatus having a coloring material ejecting head used to manufacture a color filter of a liquid crystal display, an apparatus having an electrode material (conductive paste) ejecting head used for electrode forming of an organic EL display and a face emission display (FED), an apparatus having a biological organic matter ejecting head used to manufacture biological chips, and an apparatus having a sample ejecting head as a precise pipette may be cited.
2. Description of Related Art
An ink jet recording apparatus which is a typical example of a liquid ejecting apparatus produces a comparatively low noise during printing and can form small dots at high density, so that it has been used recently in many printings including color printing.
The ink jet recording apparatus generally has an ink jet recording head (liquid ejecting head) which is loaded on a carriage and moves back and forth in the width direction (head scanning direction) of a recording medium such as recording paper and a feed means for moving the recording medium in the direction (medium feed direction) perpendicular to the head scanning direction.
In this ink jet recording apparatus, ink drops (liquid drops) are ejected from the recording head to the recording medium in correspondence to print data to print it. And, the recording head loaded on the carriage is formed so as to eject ink of colors such as black, yellow, cyan, and magenta, thereby not only text printing by black ink but also by changing the 4-color-ink ejection rate, full-color printing can be carried out.
FIG. 16 is a sectional view showing an example of the recording head of a conventional ink jet recording apparatus.
A recording head 70 has a case 71 made of synthetic resin and a flow path unit 72 stuck on the bottom of the case 71. The flow path unit 72 is formed by laminating and unifying by adhesion a nozzle plate 74 having many bored nozzle openings 73 in two rows, a flow path forming plate 75 made of silicon, an elastic plate 76, and a vibration plate 77. The bottom of the nozzle plate 74 forms a nozzle forming face 78.
The case 71 is a block member having a storing space 79 opened on the top and bottom. In the storing space 79, a pair of right and left piezoelectric actuator units 80 are installed and each of the piezoelectric actuator units 80 is fixed to the inner wall surface of the case 71 by each fixing substrate 81. To each of the actuator units 80, each tape carrier package 83 having a drive integrated circuit 82 is connected.
In the storing space 79, furthermore, as shown in FIGS. 16 and 17, between the pair of right and left piezoelectric actuator units 80, a central rib 84 is arranged. The central rib 84, at both ends thereof in the nozzle arrangement direction (the direction perpendicular to the paper surface of FIG. 16 and the vertical direction of FIG. 17), is fixed to the flow path unit 72. And, a part of the force applied to the flow path unit 72 when the piezoelectric actuator units are driven is received by the central rib 84.
Each of the piezoelectric actuator units 80 has a plurality of piezoelectric vibrators 85 arranged in one row in the nozzle arrangement direction. The piezoelectric vibrators 85 are formed by alternately laminating electrode players and piezoelectric material layers in the direction parallel with the nozzle forming face 78 and vibrate in the direction perpendicular to the lamination direction of both layers.
On the flow path forming plate 75, a plurality of pressure chambers 86 formed in two rows in the nozzle arrangement direction, a common ink chamber 87 formed for each ink kind, and an ink feed port 88 for interconnecting the pressure chambers 86 and the common ink chambers 87 for each of the pressure chambers 86 are formed. The opening on the top of each of the pressure chambers 87 is sealed by the elastic plate 76 and on the top of the part of the elastic plate 76 corresponding to each of the pressure chambers 87, an insular thick part 89 composed of a part of the vibration plate 77 is formed. The part of the elastic plate 76 corresponding to each of the pressure chambers 87 is deformed according to the deformation of the piezoelectric vibrator 85 of the piezoelectric actuator unit 80, thereby the volume of the pressure chamber 86 is changed and ink drops can be ejected from the nozzle opening 73.
In the case 71, an ink feed path 90 for feeding ink to the common ink chambers 87 are formed for each ink kind. The ink feed path 90 passes through the elastic plate 76 and interconnects to the common ink chambers 87.
As FIG. 16 shows, in the recording head of a conventional ink jet recording apparatus mentioned above, the loop of force generated when the piezoelectric vibrators 85 are expanded and contracted is completed only on the side of each of the fixing substrates 81 of the piezoelectric actuator units 80. On the opposite side of each of the fixing substrates 81, the force applied to the flow path unit 72 is received by the central rib 84 of the case 71. However, the rigidity of the central rib 84 is insufficient, so that the force cannot be received sufficiently.
Therefore, for example, in the piezoelectric actuator units 80, when the piezoelectric vibrators 85 are all driven simultaneously, the flow path unit 72 is deformed due to force generated at the time of drive and cross talk is caused. The cross talk produces an ejection characteristic difference between when a small number of piezoelectric vibrators 85 are driven and when a large number of piezoelectric vibrators 85 are driven.
Further, in a conventional recording head, due to deformation of the central rib 84, the deformation is propagated also to the pressure chambers 86 in the opposite side of the drive side and so called inter-row cross talk may be generated.
For example, in Japanese Patent Laid-Open Publication No. 2001-71486, to prevent deformation and vibration of the central rib, a method for inserting a metal into the central rib is proposed (FIGS. 1 and 2 of the publication). By this method, a cross talk prevention effect may be obtained to some extent, though another problem arises that the manufacturing steps are complicated and the manufacturing cost is increased.
Further, as shown in FIG. 16, in the conventional recording head, the fixing substrates 81 are joined to the case 71, so that to the case 71, in addition to the function of ink feed to the flow path unit 72 and protection of the piezoelectric actuator units 80, the rigidity of receiving force generated when the piezoelectric vibrators 85 are driven and of preventing deformation and the high dimensional accuracy for positioning the piezoelectric vibrators 85 with high accuracy are required. Therefore, conventionally, for example, using a material that thermoset epoxy resin is kneaded with a glass fiber as a filler, the case 71 is manufactured by injection molding.
However, use of this manufacturing method causes problems that as compared with a case of general plastics, the material cost is increased, and the molding ability is low due to kneading of a filler, and the yielding rate is reduced, and the manufacturing cost is increased.
Further, the case 71 made of resin is different in the coefficient of linear expansion from the flow path forming plate 75 made of silicon and the piezoelectric vibrators 85. Furthermore, since the case 71 is made of resin, moisture absorption expansion is caused at high humidity. Under such conditions, if the case is made of general plastics, the rigidity thereof is low, so that the case is easily deformed and follows the flow path forming substrate 75 and the piezoelectric vibrators 85 which are highly rigid, thus the members will not be peeled off from each other. However, as mentioned above, since the case 71 is made of a highly rigid material, a problem arises that the case is not deformed easily and the members are peeled off from each other.